I recall reading that there can be problems in Apache versions before 2. My server has Apache 1.3.34 (Unix) installed. Removing the %category% to make https://www.domain.com/%postname% results in the same problem, however.
(Please do post a reply if you can, but, if your solution does require manual editing of important files on the server, I would appreciate as much detail as possible. I’m new to this. Again, I am extremely grateful for your time.)
Uzer